A rack system is a term commonly used in the art to define a system or method for assembling structural members into a skeleton shape (i.e. similar to an erector set) which supports goods typically set on pallets in a warehouse. As used herein, "rack" systems include not only such systems but any structural assembly for supporting loads such as piping or electrical conduit or even when used for building structures.
Rack systems are assembled with column to beam connections. These connections typically include fasteners such as bolt and nut connections or welded connections or a combination thereof. The connections are critical to the structural integrity of the systems both for rigidity, shock loading, vibrations and sidesway. If the connection is not structurally sound, uneven loading on the rack can induce sidesway which in turn induces loads in the individual structural members for which they were not designed, causing deformation, bending, collapse, etc. Vibration loads must be an important consideration in racks, especially when used for supporting piping systems or when positioned near heavy machinery. Shock or impact loading, such as when pallets are dropped on the rack or the rack is rammed by forklift trucks must also be considered.
Another problem with conventional rack systems is in the safety of assembly and disassembly. Workmen must sometimes work at elevations of 20 feet or more. Current assemblies require workmen constantly working with both hands, which does not allow safe movement without the possibility of a fall.
The prior art has recognized the importance of a secure connection to the integrity of a rack system. Welding, in combination with gusset plates, lateral bracing, or cross bracing either at the connection or between load bearing members helps reduce sidesway. However, welded connections are generally only 20% as strong as bolted connections. Additionally, proper welds require skilled craftsmen, are labor and cost intensive, and unsuited for non-destructive disassembly.
In an attempt to solve some of these problems, Konstant et al U.S. Pat. No. 4,678,091 discloses a beam to column connection where a bolt is inserted at an acute angle through overlapping holes aligned in offset relation and the members are drawn together upon tightening of the fastener. As the nut is tightened, the offset holes are brought closer into alignment and the members laterally move into abutting contact with one another. It is difficult, in Konstant, to insert the bolt into the offset holes, especially for long and/or heavy members. In addition, Konstant produces a weak bolt connection in that a bending moment shear stress is induced in the bolt because the bolt holes must be large enough to accommodate a bolt at an acute angle. Perhaps, more significantly, as the connection is tightened in Konstant, the bolt approaches perpendicular alignment. However, the connected structural members will not be drawn into surface to surface contact with one another at the bolted connection. Thus, sidesway can still be induced.
An attempt to improve Konstant's system is disclosed in Klein U.S. Pat. No. 5,020,678 which uses a one bolt connection with a nut having a cam surface adapted to engage the inside surface of the flange of a structural member such as a channel or an angle. As the bolt is tightened, the members are wedged together into abutment as the nut is axially drawn along the threaded stud in contact with the flange which is increasing in thickness. Assembly in Klein is difficult because the cam nut must be accurately positioned before tightening. In addition, Klein, as is the case in Konstant, must have larger bolt hole diameters than what is normally established for bolted connections which induce excessive shear stresses on the bolt. Perhaps, more importantly, Klein, as in Konstant, cannot draw the two members tightly together at the bolted connection since they have been transversely shifted into abutment (or if the members are drawn tightly together at the bolted connection then they have not laterally shifted into abutting contact). Thus, Klein also does not address the sidesway problem.